1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system and a method of manufacturing such a magnetic head, and to a head assembly and a hard disk drive each of which includes the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
For magnetic read/write devices such as magnetic disk drives, higher recording density has been constantly required to achieve a higher storage capacity and smaller dimensions. Typically, magnetic heads used in magnetic read/write devices are those having a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
Write heads include those of a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and those of a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. Recently, the shift from the longitudinal magnetic recording system to the perpendicular magnetic recording system has been promoted in order to achieve higher recording density of magnetic read/write devices.
A write head for the perpendicular magnetic recording system includes a coil for generating a magnetic field corresponding to data to be written on a recording medium, and a pole layer for allowing a magnetic flux corresponding to the magnetic field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer has an end face located in a medium facing surface, and the width of this end face defines the track width.
As one of magnetic heads for perpendicular magnetic recording, there is known a magnetic head including a first and a second shield disposed to sandwich the pole layer, as disclosed in U.S. Patent Application Publication No. 2006/0203384 A1, for example. In this magnetic head, an end face of the first shield is located in the medium facing surface at a position backward of the end face of the pole layer along the direction of travel of the recording medium with a specific distance provided therebetween. An end face of the second shield is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific distance provided therebetween. The first and the second shield have a function of preventing a magnetic flux from reaching the recording medium, the magnetic flux having been generated from the end face of the pole layer and expanding in directions except the direction orthogonal to the surface of the recording medium. A magnetic head including such a first shield and a second shield is capable of attaining a higher recording density.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, if the above-mentioned skew occurs, there arise problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this is hereinafter called adjacent track erase), or unwanted writing performed between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erase. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
As one of techniques for preventing the problems resulting from the skew described above, there is known a technique in which the end face of the pole layer located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in U.S. Patent Application Publication No. 2002/0034043 A1 and JP 2006-147010A, for example. According to this technique, however, the cross-sectional area of the pole layer perpendicular to the direction in which magnetic flux flows is reduced in a neighborhood of the medium facing surface. As a result, the pole layer becomes unable to introduce magnetic flux of great magnitude to the medium facing surface, and this results in degradation of write characteristics such as overwrite property, which is a parameter indicating an overwriting capability.
To solve the problems resulting from the skew, it is also effective to reduce the thickness of the pole layer taken in the medium facing surface. However, if the entire pole layer is made thin, the cross-sectional area of the pole layer perpendicular to the direction in which magnetic flux flows is reduced. In this case also, the pole layer becomes unable to introduce magnetic flux of great magnitude to the medium facing surface, and this results in degradation of write characteristics such as overwrite property.
U.S. Patent Application Publication No. 2002/0034043 A1 discloses a technique of making the thickness of a portion of the pole layer (the main pole) near the medium facing surface decrease with decreasing distance from the medium facing surface. However, this technique has a disadvantage that, if the position of the medium facing surface varies when the medium facing surface is formed by polishing, the thickness of the pole layer taken in the medium facing surface varies and the write characteristics thereby vary.
JP 2006-147010A discloses a pole layer made up of a stack of a bottom auxiliary pole layer, a main pole layer and a top auxiliary pole layer. The bottom auxiliary pole layer touches a region of the bottom surface of the main pole layer away from the medium facing surface, while the top auxiliary pole layer touches a region of the top surface of the main pole layer away from the medium facing surface. In this pole layer, a stepped portion is formed in each of the top surface and the bottom surface such that the thickness of the pole layer taken at a position away from the medium facing surface is greater than the thickness of the pole layer taken in the medium facing surface.
Here, consideration is given to a case of forming a stepped portion in the bottom surface of the pole layer of a magnetic head having a first shield and a second shield, the first shield being located closer to the substrate than is the second shield, so as to make the thickness of the pole layer taken at a position away from the medium facing surface greater than the thickness of the pole layer taken in the medium facing surface. In this case, flux leakage from the stepped portion of the bottom surface of the pole layer to the first shield can occur. The degree of this leakage varies depending on the positional relationship between the first shield and the stepped portion of the bottom surface of the pole layer. Furthermore, the write characteristics of the magnetic head vary depending on the degree of this flux leakage. Accordingly, the positional relationship between the first shield and the stepped portion of the bottom surface of the pole layer has an influence on the write characteristics. To control the write characteristics accurately, it is therefore important to accurately define the positional relationship between the first shield and the stepped portion of the bottom surface of the pole layer.